This invention relates generally to glucose sensors for monitoring glucose concentration level in a patient fluid, such as blood. More specifically, this invention relates to an improved glucose sensor having one or more optical fiber optrodes for monitoring glucose concentration, wherein the optrodes are incorporated into a compact sensor probe adapted for in vivo implantation.
A variety of test systems and methods are known in the medical arts for measuring glucose concentration in a patient body fluid, such as blood, urine, etc. Glucose monitoring provides a valuable indicator of patient condition, and is particularly important for diabetic patients to provide an indicator of patient response to and/or compliance with a prescribed treatment regimen.
In accordance with one known and commonly used glucose detection method, an enzymatic assay is performed wherein an enzyme such as glucose oxidase is used to catalyze glucose within a patient fluid in the presence of oxygen (O.sub.2). This enzymatic reaction produces gluconic acid and hydrogen peroxide (H.sub.2 O.sub.2). Monitoring of the patient fluid before and after the enzymatic reaction can provide an indication of oxygen (O.sub.2) depletion which can be correlated substantially linearly with glucose concentration level. In the past, oxygen depletion has been measured by monitoring fluid conductivity changes. Oxygen concentration levels in body fluids have also been measured by optical monitoring of a fluorescing dye having a light output responsive to oxygen level. The enzymatic assay, as described above, has typically been performed on a patient fluid which has been drawn from the patient and transported to a medical laboratory.
In recent years, significant interest has arisen in the development of a glucose sensor adapted for in vivo implantation to provide continuous or frequent glucose measurements, particularly for providing immediate and accurate glucose monitoring for diabetic patients and the like over an extended time period. In this regard, considerable research and design effort has been directed to in vivo performance of an enzymatic assay. Unfortunately, a glucose oxidase reaction requires a stoichiometric excess of oxygen (O.sub.2) in order to yield an accurate indication of glucose concentration, but human blood has a substantial deficiency of oxygen. Although sensors have been developed with differential diffusion components aimed at insuring the presence of excess oxygen at a reaction site, such sensors have utilized electrochemical wire electrodes to measure fluid conductivity changes. This use of wire electrodes inherently requires conductive leads for passing electrical signals into the body of the patient, wherein these electrical signals must be appropriately shielded and/or filtered to minimize or eliminate inaccuracies attributable to electrical interference. As a result, electrode glucose sensors have been difficult in implement in a desirably compact and cost-efficient sensor package which can economically be discarded after use.
There exists, therefore, a need for further improvements in glucose sensors of a type adapted for in vivo implantation, wherein a sensor probe includes alternative means for monitoring an in vivo enzymatic reaction in the presence of excess oxygen. The present invention, which includes optical sensor means, fulfills this need and provides further related advantages.